Variable resistance control using mercury contact

ABSTRACT

A variable electrical resistance device such as a potentiometer, rheostat or the like, containing spaced electrical resistive and conductive elements having terminals for connection to an external electrical circuit, and a contact of electrically conductive liquid, such as mercury, which spans the elements to provide a current path between the elements and is confined for relative movement along the elements to vary the electrical resistance between the terminals. In the disclosed embodiment, the resistive and conductive elements are carried by a rotor which is rotatable to effect movement of the elements past the mercury contact.

Lawrence, J r.

[ Dec. 25, 1973 VARIABLE RESISTANCE CONTROL USING MERCURY CONTACT Inventor:

Filed:

James F. Lawrence, Jr., 13161 Barret Hill Cir., Santa Ana, Calif. 92705 Nov. 10, 1971 Appl. No.: 197,414

US. Cl. 338/151, 338/94, 338/97 Int. Cl HOlc 5/00 Field of Search 338/151, 156, 44, 338/94, 97; 323/98 References Cited UNITED STATES PATENTS Primary ExaminerBemard A. Gilheany Assistant Examiner-D. A. Tone Att0rneyForrest J. Lilly [57] ABSTRACT A variable electrical resistance device such as a poten tiometer, rheostat or the like, containing spaced electrical resistive and conductive elements having terminals for connection to an external electrical circuit, and a contact of electrically conductive liquid, such as mercury, which spans the elements to provide a current path between the elements and is confined for relative movement along the elements to vary the electrical resistance between the terminals. In the disclosed embodiment, the resistive and conductive elements are carried by a rotor which is rotatable t0 effect movement of the elements past the mercury contact.

11 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates generally to variable electrical resistance devices and more particularly to such a device wherein the resistor engaging contact is a globule I of mercury or other conductive liquid.

SUMMARY OF THE INVENTION The variable electrical resistance device of this invention has spaced electrical resistive and conductive elements with terminals for connection to an external electrical circuit, and a globule of electrically conductive liquid, such as mercury, spanning the elements to provide an electrical current path between the elements. This globule is referred to herein as a liquid or mercury contact. The liquid contact is confined for relative movement along the resistive and conductive elements to vary the electrical resistance between the terminals.

In the particular physical embodiment selected for illustration, the resistive and conductive elements are carried by a rotor having a normally generally horizontal axis. The liquid contact, in this case a mercury contact, is confined within a generally annular channel which is concentric with the rotor axis and exposes the resistive and conductive elements to the mercury contact. When the rotor is turned, gravity retains the mercury contact at the bottom of the channel, and the resistive and conductive elements rotate past the contact to vary the effective electrical resistance between the terminals of the resistance device. A wall extends across an upper portion of the mercury channel and a restricted passage communicates the channel ends at opposite sides of the wall to provide a viscous damping effect on the mercury contact.

The conductive elements of the disclosed embodiment is a second resistive element electrically joined at one end to an end of the first resistive element. The opposite ends of the elements are connected to the terminals of the resistance device, such that the device is effectively a rheostat. As will appear from the ensuing description, the device may be arranged to form other types of resistance devices, such as a potentiometer or a T-attenuator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal section through a variable resistance device according to the invention;

H6. 2 is a section taken in line 2-2 in FIG. 1; FIG. 3 is a perspective view ofa wire wound resistor assembly embodied in the device; and

FIG. 4 is a schematic circuit diagram of the device.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawings illustrate a variable electrical resistance device 10 according to the invention having a housing 12 with external terminals 14 for connection to an external electrical circuit. Contained within the housing are spaced electrical resistive and conductive elements 16, 18 connected to the terminals 14, respectively, and a globule 20 of electrically conductive liquid, in this instance mercury. The mercury globule 20 is contained with a closed channel 22 in the housing which exposes the resistive and conductive elements l6, 18 for contact by the mercury. The mercury thus provides an electrical current path between the elements and, as noted earlier, is referred to herein as a liquid or mercury contact. As will appear presently, the channel 22 confines the mercury contact 20 for relative movement along the resistive and conductive elements 16, 18 to vary the electrical resistance between the terminals 14.

Referring in greater detail to the drawings, the housing 12 of the variable resistance device has a cylindrical wall 24 and an integral rear end wall 26 closing the rear end of the housing. The front end of the housing is closed by a front end wall or faceplate 28 secured by screws 30 to the cylindrical wall 24. The housing may be attached to a rear support 32 or otherwise mounted in such a way that the housing axis is generally horizontal.

Within the housing 12 is a cylindrical rotor 34. Rotor 34 has front and rear shafts 36 rotatable in bearings 38 in the housing end walls 26, 28 on the horizontal axis of the housing. The front shaft 36 projects forwardly of the faceplate 28 and mounts a knob 40 by which the rotor may be turned. The outside diameter of the rotor is somewhat less than the inside diameter of the housing to provide an annular clearance space between the rotor and housing.

Rotor 34 has an inner cylindrical body 41 with a rear outwardly directed annular flange 41a. Fitting snugly about the rotor body is a sleeve 42. A second sleeve 44 fits snugly about sleeve 42 and the rear body flange 41a. The housing 12, rotor 34, and sleeves 42, 44 are constructed of a suitable electrical insulating material, such as plastic. The rear end of sleeve 42 is spaced from the rear motor flange 41a to form the channel 22 which contains the mercury contact 20. Channel 22 is circular and centered on the horizontal axis of the housing 12 and rotor 34. The rotor body 41 and sleeves 42, 44 are sealed to one another to seal the mercury in the channel. Extending rearwardly from sleeve 42 across the upper portion of channel 22 is a wall member 45. A restricted passage 45a in the rotor body 41 communicates the ends of the channel at opposite sides of the wall member to provide a viscous damping effect on the mercury contact which is a sufficiently large globule to fill the entire channel cross section.

The resistive and conductive elements 16, 18 are wires which are wrapped spirally about a split sleeve 46 of electrical insulating material. The wires are disposed in spaced side-by-side relation so as to be insulated from one another. Sleeve 46 with its wires 16, 18 is contained within an annular cavity 48 in the sleeve 42. Cavity 48 opens rearwardly to the mercury channel 22. The rear end of the sleeve 46 projects through the open rear end of the cavity into the channel, thus closing the actually one continuous length of resistance wire which is doubled on itself to provide a non-conductive loop and wrapped about the sleeve 46 as explained above. The ends of the wires are connected to the terminals by pigtails 51 contained within the annular clearance space between the housing 12 and rotor 34 to permit turning of the rotor through its range of rotation.

When the resistance device is mounted in its illustrated horizontal position, the mercury contact occupies its illustrated position at the bottom of the channel 22. The contact then spans and engages the adjacent exposed turns of the resistance wires l6, 18 to provide a current between the wires. The mercury contact remains in its lower position during turning of the rotor 34. As a consequence, the resistance wires undergo rotation past the contact, whereby successive exposed turns of the wires are brought into electrical contact with the mercury contact. The relative movement of the mercury contact with respect to the wires thus occurs along the wires in much the same manner as the movable contact or slider of a conventional resistance device. As noted earlier, however, the present mercury contact eliminates the wear, noise and other problems associated with such sliding contacts. The restricted communicating passage 45a between the upper ends of the channel 22 provides a damping action on the mercury contact 20 to damp oscillatory motion of the contact in the channel.

As noted above, the wires 16, 18 of the present device are both resistance wires which arejoined at one end and connectedat their other ends to the terminals 14. The device thus constitutes a rheostat. In this regard, attention is directed to FIG. 4 which is a schematic circuit diagram of the device. The present variable resistance device may be arranged in other electrical configurations, such as a potentiometer in which one wire 16 or 18 is a plain conductor, or a T- attenuator having three resistance wires arranged sideby-side and three terminals connected to corresponding ends of two wires and the opposite end of the third wire.

I claim:

1. A variable electrical resistance device embodying:

an insulation rotor having a horizontal axis of rotation;

a closed annular channel in said rotor concentric with said rotor axis;

an electrically conductive liquid globule in the bottom of said channel forming an electrical contact therein, said globule staying at the bottom of said channel by gravity; and

a linear electrical resistance element extending concentrically around said rotor outside said channel, having electrical contact portions projecting into said closed channel at angularly spaced intervals therearound, so as to successively contact said globule as said rotor is turned.

2. The device according to claiml, including:

an insulation annulus on and extending annularly and concentrically around said rotor, said electrical resistance element comprising an electrical. resistance wire wound spirally around said annulus, said annulus having a concentric annular edge surface which is crossed transversely at spaced intervals by successive turns of said wire, and which is situation in continuous communication with the interior of said channel, whereby the turns of said wires which pass across said annular edge surface are exposed in said channel for contact by said globule when positioned by said rotor at the bottom.

3. The device according to claim 2, wherein:

said insulation annulus comprises an insulation sleeve concentric with said rotor axis having one edge portion projecting axially into communication with said channel, and crossed transversely by successive turns of said wire.

4. The resistance device according to claim 3,

wherein: v

the wire wound on said sleeve embodies a spiral loop.

5. The resistance device according to claim 3,

wherein:

the wire wound on said sleeve embodies a closed spiral loop, one half being resistance wire and one half a conductive wire.

6. The resistance device according to claim 3,

wherein: I

said channel is formed with an annular, concentric, laterally facing opening, said rotor having therein a concentric annular cavity which houses said sleeve, and which has portions closing said laterally facing opening into said channel, excepting for an annular opening which receives said edge portion of said sleeve into a position ofexposure to said globule in said channel.

7. The device according to claim 6, wherein:

the interior of said cavity is sealed to said channel on both sides of said edge portion of said insulation sleeve.

8. The device of claim 6, wherein:

said channel for said globule is sealed against loss of the liquid of said globule from said rotor.

9. A variable electrical resistance device according to claim 2 including:

a housing enclosing said rotor; and

a knob fixed to said rotor and accessible externally of said housing for turning said rotor.

10. The device according to claim 1, including:

a transverse wall across said channel, and a bypassing passage in said rotor communicating with said channel on opposite sides of said wall.

11. The device according to claim 1, including:-

at least one additional resistance element extending concentrically around said rotor,-out of electrical contact with said first mentioned resistance element linearly along said rotor, and having electrical contact portions projecting into said closed channel at angularly spaced intervals therearound, intervening between the spaced contact elements of said first mentioned resistance element, whereby adjacent contact elements of said two resistance elements are successively bridged as said rotor is turned. 

1. A variable electrical resistance device embodying: an insulation rotor having a horizontal axis of rotation; a closed annular channel in said rotor concentric with said rotor axis; an electrically conductive liquid globule in the bottom of said channel forming an electrical contact therein, said globule staying at the bottom of said channel by gravity; and a linear electrical resistance element extending concentrically around said rotor outside said channel, having electrical contact portions projecting into said closed channel at angularly spaced intervals therearound, so as to successively contact said globule as said rotor is turned.
 2. The device according to claim 1, including: an insulation annulus on and extending annularly and concentrically around said rotor, said electrical resistance element comprising an electrical resistance wire wound spirally around said annulus, said annulus having a concentric annular edge surface which is crossed transversely at spaced intervals by successive turns of said wire, and which is situation in continuous communication with the interior of said channel, whereby the turns of said wires which pass across said annular edge surface are exposed in said channel for contact by said globule when positioned by said rotor at the bottom.
 3. The device according to claim 2, wherein: said insulation annulus comprises an insulation sleeve concentric with said rotor axis having one edge portion projecting axially into communication with said channel, and crossed transversely by successive turns of said wire.
 4. The resistance device according to clAim 3, wherein: the wire wound on said sleeve embodies a spiral loop.
 5. The resistance device according to claim 3, wherein: the wire wound on said sleeve embodies a closed spiral loop, one half being resistance wire and one half a conductive wire.
 6. The resistance device according to claim 3, wherein: said channel is formed with an annular, concentric, laterally facing opening, said rotor having therein a concentric annular cavity which houses said sleeve, and which has portions closing said laterally facing opening into said channel, excepting for an annular opening which receives said edge portion of said sleeve into a position of exposure to said globule in said channel.
 7. The device according to claim 6, wherein: the interior of said cavity is sealed to said channel on both sides of said edge portion of said insulation sleeve.
 8. The device of claim 6, wherein: said channel for said globule is sealed against loss of the liquid of said globule from said rotor.
 9. A variable electrical resistance device according to claim 2 including: a housing enclosing said rotor; and a knob fixed to said rotor and accessible externally of said housing for turning said rotor.
 10. The device according to claim 1, including: a transverse wall across said channel, and a by-passing passage in said rotor communicating with said channel on opposite sides of said wall.
 11. The device according to claim 1, including: at least one additional resistance element extending concentrically around said rotor, out of electrical contact with said first mentioned resistance element linearly along said rotor, and having electrical contact portions projecting into said closed channel at angularly spaced intervals therearound, intervening between the spaced contact elements of said first mentioned resistance element, whereby adjacent contact elements of said two resistance elements are successively bridged as said rotor is turned. 